Comparison of Reported Condensed Consolidated Statement of Operations Under New Guidance (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Collaboration and license revenue	$ 6,038	$ 5,128
Operating expenses:
Research and development	60,067	30,645
Loss from operations	(85,300)	(40,538)
Net loss	(84,510)	(41,764)
Net loss attributable to Portola	$ (84,178)	$ (41,719)
Basic and diluted	$ (1.28)	$ (0.74)
Balances without the adoption of ASC 606 | Accounting Standards Update 2014-09
Revenues:
Collaboration and license revenue	$ 6,354
Operating expenses:
Research and development	59,345
Loss from operations	(84,262)
Net loss	(83,472)
Net loss attributable to Portola	$ (83,140)
Basic and diluted	$ (1.27)
Effect of change | Accounting Standards Update 2014-09
Revenues:
Collaboration and license revenue	$ (316)
Operating expenses:
Research and development	722
Loss from operations	(1,038)
Net loss	(1,038)
Net loss attributable to Portola	$ (1,038)
Basic and diluted	$ (0.01)